1. Field of the Invention
The present invention relates to a position sensing, manually teachable power drive for a linearly movable carriage which permits the carriage to be rapidly positioned at desired locations along its support ways or rails under programmed control.
2. Description of the Prior Art
A common technique for positioning industrial tools is to mount them to a carriage. The carriage is then driven along guide rails or ways by a ball nut and ball screw. The ball screw is a threaded shaft having a length equal to the distance the carriage must be moved and is rotatably driven by a motor. The carriage is attached to the nut and is moved along the guide rail as the shaft is rotated. Other devices have used rack and pinion drives which require a separate long rack gear.
Precise control and positioning is possible with the ball screw technique. If the ball screw is rotated too fast, however, the shaft will whip and vibrate. This, therefore, places an upper limit on the speed with which the carriage housing may be moved from position to position. What is desired therefore is a position sensing means to quickly and precisely move a carriage housing along its guide rails at speeds not limited by whipping of a ball screw shaft. This power drive unit must have readily releasable driving wheels so that the carriage can be manually moved back and forth along its guide rails for manual teaching. The position sensing element continues functioning when the driving wheels are released.
The present invention solves prior problems by eliminating the ball screw or separate rack gear. The carriage housing is driven along its guide rails by an attached power drive unit which uses friction drive rollers engaged with one of the carriage guide rails. No separate drive shaft is necessary.
U.S. Pat. No. 4,280,289 shows an underwater trenching machine which is driven along a pipe line by rollers mounted directly on the pipe. Although this structure does show the use of rollers for driving a machine along a cylindrical member, its application is significantly different from that of a carriage for moving a tool assembly.
U.S. Pat. No. 2,992,620 shows a carriage used to support measuring equipment attached to and moving along a track. The carriage includes rollers which move along the track but these rollers are not driven.
U.S. Pat. No. 3,675,583 describes a vehicle which moves about a vertical rail. Two driven wheels are engaged to opposite sides of the vertical rail and provide traction by which the vehicle may be driven.
U.S. Pat. No. 3,688,410 discloses an apparatus for measuring and displaying the amount of movement of a machine tool element. As a cylindrical rod moves a roller urged against the rod will rotate and sense the displacement of the rod.
The technique of measuring lengths in which a rotating element is urged against the item to be measured is also shown in U.S. Pat. Nos. 2,867,908, 3,318,005, 3,561,120, and 3,972,124.
There is a continuing need for improvement in tool carriage drives. The carriages must be capable of quick response and precise positioning. The carriage should also be easily interfaced to a computerized control system and manual teaching capability is very desirable.